Stents are prosthetic devices implanted within a subject's vessel lumen to maintain the patency of the vessel. Typically stents are comprised of cylindrical members, which are capable of expanding from a smaller diameter to a larger diameter. The stent is typically implanted within a patient's vasculature by a minimally invasive procedure using a catheter and guide wire. The catheter serves as a delivery device to transport the stent to its implantation site, e.g. an occluded vessel lumen. Once delivered to the desired site, the stent is expanded from its smaller delivery diameter to its larger diameter. A balloon-expandable stent is caused to expand by inflating the underlying balloon located at the distal end of the catheter, and a self-expanding stent is allowed to expand by releasing it from a sheath located at the distal end of the catheter. Ultimately, the stent is deployed against the interior lining of subject's vessel wall. The expansion force of the expanded stent expansion opens up the vessel occlusion. The structural integrity of the stent operates as scaffolding to support the vessel lumen and maintain its patency.
A variety of vascular stents are known, such as U.S. Pat. No. 3,657,744 (Ersek), U.S. Pat. No. 3,868,956 (Alfidi), U.S. Pat. No. 4,441,216 (Ionescu), U.S. Pat. No. 4,503,569 (Dotter), U.S. Pat. No. 4,512,338 (Blako), U.S. Pat. No. 4,553,545 (Maass), U.S. Pat. No. 4,580,568 (Gianturco), U.S. Pat. No. 4,733,665 (Palmaz), U.S. Pat. No. 4,762,128 (Rosenbluth), U.S. Pat. No. 4,800,882 (Gianturco), U.S. Pat. No. 4,856,516 (Hillstead), U.S. Pat. No. 4,886,062 (Wiktor), U.S. Pat. No. 5,421,955 (Lau), U.S. Pat. No. 5,476,508 (Amstrup), U.S. Pat. No. 5,514,154 (Lau), U.S. Pat. No. 5,449,373 (Pinchasik), U.S. Pat. No. 5,695,516 (Fischell), U.S. Pat. No. 6,231,598 (Berry).
Because stents are usually deployed through a subject's vasculature, which can often involve navigating through both narrow and curved vessels, it is advantageous for the stent to be flexible along its longitudinal axis. Loading conditions generate significant amounts of stress on the stent involving torsion, extension, compression and flexion. Once deployed, the stent must have sufficient radial strength to resist compressive forces in order to maintain vessel patency. In addition, where the stent is deployed in a vessel, which undergoes regular stress such as by bending or where the vessel itself is curved, flexibility and resistance to fracture of the deployed stent may also be important.
A need exists for an improved stent design that will provide sufficient radial strength to maintain vessel patency while at the same time provides sufficient flexibility to facilitate easy deployment and accommodation of the particular physiological stress factors associated with the vessel in which it is deployed while also resisting fatigue fracture as a result of those same stress factors. Further, a need exists for a modular stent that is capable of separating at predetermined points in response to stress, in lieu of fracturing haphazardly. Embodiments of the invention described below meets these needs as well.